1. Field
The present invention relates to reducing optical losses of bulbs used for lighting, and more particularly, to the use of anti-reflective coatings on the inner and outer surfaces of the shells of the bulb in order match the index of refraction of the shell material to the indices of refraction of the inside/inner portion of the bulb and outside/ambient surroundings of the bulb, thus increasing the light output of the bulb being replaced.
2. Description of Related Art
There are several types of light bulb now in use. The most common is still the incandescent bulb, formed by surrounding a very hot filament in a partial vacuum with a glass shell. Another common type is the fluorescent bulb, formed by surrounding a plasma column with a glass shell containing a phosphor, the phosphor serving to convert the ultraviolet radiation emitted by the plasma into visible light. Another type of bulb, rapidly gaining in popularity, is the LED (light emitting diode) bulb. One popular method of forming an LED bulb is to surround the LEDs with air or a fluid, gel or plastic, and encase the LEDs inside a plastic shell.
All of these bulbs share in common the fact that their light source is surrounded, either immediately or with an intermediate, by a shell. The shell provides physical protection to the light source from the surrounding ambient air, as neither the partial vacuum of an incandescent filament, nor the plasma column of a fluorescent, nor the fluid, gel or plastic of an LED bulb will normally withstand direct exposure to ambient air (or ambient surroundings). In the case of air surrounding the LEDs in an LED bulb, the shell provides physical isolation of the LEDs from physical damage. While the shell provides physical isolation for the internal components of the bulb, it has the drawback that the commonly used shell materials, glass or plastic, have a different index of refraction than does the surrounding ambient air (or ambient surroundings). Further, in the case of the LED bulb using a fluid, gel or plastic, the index of refraction of the shell does not match that of the internal fluid, gel or plastic either. This mismatch of index of refraction creates reflection of the impinging light at the material interface, resulting in loss of light output.
This invention has the object of developing a light emitting apparatus, such that the above-described primary problem is effectively solved. In accordance with an exemplary embodiment, the light emitting apparatus provides a bulb constructed similarly to that of currently available bulbs, but without the light losses associated with reflections from the shell enclosing the bulb. In accordance with an embodiment, the bulb includes a shell, constructed of glass or plastic. The shell has an anti-reflective coating on the inside (i.e., an inner surface) and/or outside (i.e., an outer surface) of the shell. In accordance with an exemplary embodiment, the anti-reflective coatings are designed such that reflections from the interfaces from the inside to the shell, and from the shell to the ambient air or ambient surroundings are minimized.